PrintGig

Why fillets matter in 3D printing

A lot of part failures start at one place:

# Sharp corners.
- That is where stress concentrates.
- Not the whole part.
- Just that tiny corner.

In 3D printing, that matters a lot.

# A small fillet can:
- Reduce stress concentration.
- Spread load more evenly.
- Improve durability.
- Lower the risk of cracks starting at the corner.

A sharp corner looks clean in CAD.
But in the real world, it is often the weakest point.

One simple rule:
If the part carries load, do not leave a sharp corner there.
Fillets are not just for looks.
They are part of good engineering design.

How to design for 3D printing — the real decisions that change the part

3D printing isn’t just “you send a file, we print it.”
It’s our combined effort to deliver the best components.

👉 1. Orientation controls strength
- FDM parts are weakest between layers.
- Strongest when load follows the print direction.
- Decide orientation based on force path, not “what looks easiest”.

👉 2. Overhang = support = cost
- Overhangs beyond ~45° usually need support.
- More support → more time, more material, worse surface.
- Use slopes, chamfers, or small ribs instead of long vertical faces.

👉 3. Wall thickness should be functional, not random
- Too thin → weak, fragile, prone to warping.
- Too thick → slow print, high cost, no extra benefit.
- Use 1–2 mm for light parts, 2–4 mm for functional parts unless load really requires more.

👉 4. Tolerance is not precision machining
- 3D printing has real build variation.
- Designing “perfect fit” usually means “no fit”.
- Give moving parts 0.2–0.5 mm clearance; tight fits 0.1–0.2 mm max.

👉 5. Fillets beat sharp corners
- Sharp corners concentrate stress → cracks start here.
- Add radius wherever the part carries load.
- Even small fillets improve fatigue life and stress distribution.

One rule to remember
Design for how the part will be printed, not just how it looks in CAD.
A small change in geometry can change:
– print success
– strength
– cost
– lead time
– post processing

Come talk to us to discuss your next project!